This disclosure concerns television picture tubes of the type requiring one or more high voltages for operation, and a means for introducing such a voltage into the picture tube.
Electron guns used in television picture tubes usually require a high voltage for operation. In present-day, high-brightness color picture tubes, this "ultor anode" voltage may be 30 kilovolts or higher. In standard practice, this voltage is introduced into the picture tube envelope through an anode button that extends through the tube funnel. An electrical path within the tube conducts the high voltage to at least one high voltage anode electrode of the electron gun.
Recently developed electron guns, such as described in U.S. Pat. No. 3,895,253, assigned to the assignee of this invention, may require a secondary high voltage. This secondary high voltage may be in the range of, for example, 11 to 18 kilovolts.
Problems may arise in introducing a secondary voltage of this magnitude into the tube envelope. A button similar to the anode button in the funnel, but extending through the neck, can be used; however, this appreciably increases the cost of manufacture. Another way of introducing a secondary voltage is by conduction through a lead-in pin located in the base of the tube. The use of this method, however, may result in arcing problems because of the close propinquity of the pins in present-day tubes.
The problem of arcing in the pin area is further aggravated by the need for high-voltage conditioning, or "spot-knocking" of electron guns. This is a process whereby a very high direct-current voltage, usually in the range of thirty to fifty kilovolts is conducted through the afore-described high-voltage pin. This high voltage may contain in addition an increment of pulsed radio frequency voltage. These potentials are applied to deliberately induce benign arcing between the electrodes, as such arcing removes or "knocks" minute electrode protrusions or unwanted particles ("spots"), which could act as potential arc paths if allowed to remain on the electrodes. To prevent arcing between the pins during this "spot-knocking" procedure, the base of the tube under test is usually immersed in an electrically inert liquid of high dielectric strength.
A means for arc-prevention between lead-in pins is described and claimed in referent copending application Ser. No. 756,204. Arc-prevention is achieved during conditioning and during normal operation of the tube by the provision of an extended, yet axially compact, arc path length between the relatively high-voltage pins and between the high-voltage pins and adjacent relatively low-voltage pins.
Sokolov in U.S. Pat. No. 2,667,528 addressed the problem of introducing a high-voltage lead into the evacuated envelope of a small, radio-type electron tube. The disclosed tube comprises a structure wherein a high voltage lead is brought out of the tube envelope through an exhaust tubulation, the tip and the tube key. Provision is made for connecting circuit wiring to the lead by means of a cap and socket connector. The technique is not known to be utilized in television picture tubes and indeed is not believed to be susceptible to use in such tubes.
A prior art apparatus for evacuating a television picture tube is shown by FIG. 1. A base section 10 of a television cathode ray tube (not shown) in preparation for evacuation will be readily recognized by those skilled in the art. A plurality of lead-in pins 12 are represented schematically. In the process of evacuation, an exhaust tubulation 14 is inserted into the vacuum port 16 of vacuum pump 18, shown in highly schematic form. A pliable seal 20, which may be in the form of an O-ring, provides an air-tight connection between tubulation 14 and vacuum port 16.
Vacuum pump 18 withdraws the air from the interior of the cathode ray tube envelope, as indicated by arrow 22. When the desired vacuum has been obtained; that is, a vacuum of about 10.sup.-6 torr, tip-off oven 24, indicated schematically, is positioned as shown. Incorporated within tip-off oven 24 is a resistive element energized by an electric current. When energized, the resistive element heats tip-off oven 24 and softens the glass of tubulation 14. The vacuum within the cathode ray tube envelope causes the softened glass to be pulled inwardly; the subsequent shape is shown by 26, and is commonly termed a "pinch-off." The tubulation 14 is conventionally then cut off at the point indicated by arrows 28 by circumferentially scoring the tubulation and flexing it, causing it to break off.